The present invention generally relates to a boring attachment for a drilling and milling machine, lathe or other automatic machine of this general type.
Such boring attachments have been known for some time and are used for the precision machining of bores with diameters smaller than 50 mm. To this end, a boring tool with a cylindrical clamping shaft is used, which is coaxially clamped in the forward end of a boring head to provide an effective cutting edge (preferably formed of a high-speed machining steel, hard alloy, or other cutting material, or as a reversible carbide tip). Fine adjustment of such boring tools is performed by transverse displacement of the cutting edge using an appropriate mechanism.
Boring attachments of this general type are known from CH-A No. 508,440 and DE-GM No. 74 38 172, but can only be used at relatively low rotation speeds. Since new cutting-edge-forming materials with higher heat resistance have been available for some time, much higher speeds would ordinarily be possible, which would permit a considerable savings in operating time. However, vibration, which is the consequence of an imbalance (loading) which inherently develops upon displacement of the boring tool, tends to reduce the precision of such borings (with good surface finish) at the high speeds which would ordinarily be permissible for such new cutting materials.
To eliminate this imbalance (loading), DE-A No. 35 10 259 suggests mounting a balancing device on the boring attachment which has balancing weights in the shape of circular disk segments and which can be pivoted from their initial position around a common fulcrum point by means of pull-cords attached to the segment bodies. However, such a balancing device inherently increases the overall height of the boring head and requires grooves which reduce the stability of the boring head. It is also a disadvantage that the balancing device must be readjusted after each significant adjustment of the boring tool. Experience has shown that this readjustment is often omitted, through negligence, which can cause damage to the workpiece.
What is more, boring tools with different lengths, and consequently with different weights, must be used for different machining depths. It has been found that these differences in weight can be only partially compensated for with the abovementioned balancing device. Because of this, only a limited number of boring tools are available, as a consequence of which these tools are often either too short or too long for their particular practical application. This is significant since every millimeter of excess length of the boring tool causes an impairment of its vibration characteristics, and accordingly the surface finish of the bore to be machined, or makes it necessary to resort to lower operating speeds and hence a less economical operation.